s390/pci: ioremap() align with generic code

Let's use the same signature and parameter names as in the generic
ioremap() definition making the physical address' type explicit.

Add a check against address wrap around as in the generic
lib/ioremap.c:ioremap_prot() code.

Finally use free_vm_area() instead of vunmap() as in the generic code.
Besides being clearer free_vm_area() can also skip a few additional
checks compared with vunmap().

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>